Continuous mill control means



1963 R. w. BARNITZ ETAL 3,109,330

CONTINUOUS MILL CONTROL MEANS Filed Aug. 2.4, 1960 INVENTORS Richard W.Bornitz 8 John F. McC'Orthy B Ma ATTORNEY 000 0 Ooomooo .l l 1 oooooooNu mm #0 no 8. 3.2.0

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United States Patent 3,109,330 CONTINUOUS MILL CONTROL MEAN Richard W.Barnitz and John F. McCarthy, Pittsburgh, Pa., assignors to Jones &Laughlin Steel Corporation, Pittsburgh, Pa a corporation of PennsylvaniaFiled Aug. 24, 1960, Ser. No. 51,586 4 Claims. (Cl. 8tl-35) Thisinvention relates to apparatus for rolling hot metal slabs and the likeat high speed to minimize gage variations between the leading andtrailing portions of the rolled product. More particularly, theinvention relates to a rolling procedure wherein the rolling mill isinitially operated at a relatively low speed to permit the forward endof the rolled product to pass over a run-out table and become attachedto a coiler, followed by an increase in the speed of the mill tominimize the required rolling time.

Although not limited thereto, the present invention is particularlyadapted for use with continuous hot strip mills. In such mills, a steelslab or the like is first heated to the proper rolling temperature andthereafter conveyed through one or more scalebreakers and roughingstands to a plurality of tandem finishing stands where the metal isprogressively rolled to the final gage. As the rolled strip proceedsfrom the last tandem finishing stand, it is carried over a long table,called the run-out table, which consists of individually driven rollershaving a plurality of water sprays positioned overhead to cool the stripas it passes thereby. From'the run-out table, the strip is fed to acoiler where it is wound into coils for shipment or further processing.

In a continuous hot strip mill of the type described above, gagevariations normally occur between the leading and trailing portions ofthe rolled product. That is to say, the gage will usually be greater atthe trailing portion of the strip. One of the primary causes of gagevariation is the temperature dillerential along the length oi the strip.As the slab is rolled, it continuously cools, meaning that the trailingportion of the strip to be rolled will be cooler and less ductile thanthe forward portion. This, of course, results in a gradual increase ingage along the length of the strip.

Gage variations due to the aforesaid temperature differential may beminimized by increasing the speed of the rolling mill. Previous to thisinvention, however, continuous hot mills were normally operated at aconstant speed throughout the rolling operation; and this speed waslimited primarily by the permissible entry speed of the strip into thecoiler. As was mentioned above, the forward end of the rolled strip,after leaving the last finishing stand, passes over a run-out tablebefore being directed into a coiler which automatically grips the end ofthe strip and places it under tension. As the strip passes over therun-outtable before being attached to the coiler, it isefiect-ivelypushed from behind by the rolling mill while its forward endis tree, the result being that if the speed of the mill istoo greatthe-strip'will buckle and possibly run off the table before beingattached to the coiler. This problem is particularly acute in thecase ofstrip of narrow width such as skelp used in the manufacture of seamwelded tubular products. j

Thus, the speed of prior art rolling mills, being constant during theentire rolling procedure, was determined by the maximum permissiblecoiler entry speed, notwithstanding the fact that this speed might bebelow the maximum speedof the mill where the gage variation referred toabove could be minimized.

As a primary object, the present invention provides apparatus forcontinuously rolling hot strip wherein temperature and gage variationsbetween the leading and trailing portions of the strip are minimized.

3,109,339 Patented Nov. 5, 1963 Another object of the invention is toprovide a system of the type described above in which the speed of therolling mill is initially maintained at a relatively low value tofacilitate entry of the end of the strip into the coiler and thereafterincreased to minimize the required rolling time.

In accordance with the invention, hereafter described, the rolling millis initially operated at a low speed until the forward end of the strippasses over the run out table and is fed into the coiler. Thereafter,when the forward end of the product is attached to the coiler and theproblem of guiding the free end of the strip is no longer present, themill speed is increased to decrease the amount of time required to rollan entire slab and thereby minimize any gage variations along the lengthof the strip. As will be understood, this procedure also allows largerand heavier slabs to be rolled since the cooling time is reduced.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying single FIGURE drawing which schematicallyillustrates the operation of the invention.

Referring now to the drawing, which is for the purpose of illustratingan embodiment of the invention and not for the purpose of limiting thesame, a heated steel slab 10 on conveyor 12 is first passed through oneor more roughing stands, schematically illustrated at 14, to ascalebreaker 16. From the scalebreake-r 16 the slab 10 is passed througha plurality of tandem finishing stands S1-S6, it being understood thatonly three stands S1S2 and S6 are shown herein. Each of the finishingstands 81-86 is provided with an individual direct current drive motor,the drive motor for stand S1 being indicated at M1 and the drive motorfor stand S6 being indicated at M6. Motors M1 and M6, as well as themotors for the other stands, are provided with external control windings18 which are connected to motor control circuits, generally indicated at20. The motors M1 and M6 are also provided with series windings 22 andare connected to indi vidual direct current generators G1 and G6,respectively. As will be understood, the various drive motors for theother finishing stands are also provided with their direct currentgenerators. Generators G1 and G6 are driven by three-phasealternating-current motors A1 and A6, respectively, substantially asshown. The generators G1 and G6 are also provided with field windings 24which are connected to individual generator control circuits, indicatedat 26. The generator control circuits 26 for each mill stand are, inturn, connected to a master pilot regulator circuit 28, the arrangementbeing such that the output of regulator 28 will control the fieldsproduced by windings 24 and, hence, the output voltages or generatorsG1, G6 and the generators, not shown, associated with the other stands.The output of the master pilot regulator 28 is controlled by apotentiometer 3b which is connected through mechanical linkage 32 to apilot motor 34. With this arrangement, when the motor 34 rotates, itwill vary the position of the movable contact on the potentiometer 30whereby the output voltages of the generators G1 and G6 will be variedto regulate the speed of motors M l M6. After the leading end of therolled strip passes through the last finishing stand S6, it must travelover a run-out table 36 before being deflected by a deflector 38 into acoiler 40. Above the run-out table 36 are a plurality of water sprays 42which cool the strip as it passes thereby. The coiler 40, well known inthe art, automatically grasps the end of the strip and thereafterrotates to place the material in tension. However, when the forward endof the strip initially passes through stand S6, it must be pushed overthe run-out table 36 by the metal following it until said end reachesthe coiler 40 where it may be grasped to place the strip under tension.If the speed of the rolling mill is too great during the time that 3 vthe forward end of the strip passes over run-out table 36, it may buckleor possibly run off the table. Consequently, during this time, the speedof the mill must be adjusted whereby the end of the strip may besuccessfiully guided onto coiler 40.

As was explained above, most prior art rolling mills were normallyoperated at a constant speed throughout the rolling operation. Since theslab 10 will cool down during rolling, the latter part of the slab whichis rolled 'is cooler and less ductile than the first part to be rolled,

resulting in a gradual increase in gage along the length of the strip.This variation in gage may be minimized by increasing the speed of themill, but if the mill is operated at a constant speed, in accordancewith previous practice, this speed is limited by the maximum permissibleentry speed of the strip into the coiler 40.

In accordance with the present invention, the rolling mill comprisingstands S1, S6, etc., is initially operated at a relatively low speeduntil the end of the strip passes over the run-out table 36 and-isattached to the coiler 4t I of the circuit whereby the field produced bywinding 76 is at a maximum. Output terminal82 of amplidyne 72 may beconnected to one side of the pilot motor 34 through the normally closedcontacts 84 of a mill down normally open contacts '92 of relay M'U. Inparallel with relay MU is a holding coil MDH for relay MD; and,similarly, in parallel with relay MD is a holding coil MUH for relay MU.With this arrangement when relay MU is energized, for example, coil MDHwill lock relay MD in its deenergized position wherein contacts 84 areclosed and contacts 9% are open. Similarly, when relay MD is energized,holding coil MUH will hold relay MU in deenergized condition whereincontacts 86 are closed Thereafter, the speed of the mill is increased tominimize the time required for the slab 10 to pass through the'mill andthereby reduce any variation in gage between the leading and trailingportions of the strip. To effect this procedure, circuit means includingload relays lLR and and 6LR are provided. Load relay lLR is connected inshunt with the series field winding 22 for motor M1 and will beenergized when the load on this motor increases. That is, it will beenergized when the leading end of the slab initially passes throughstand S1. Similarly, a load relay 6LR in shunt with the series winding22 for motor M6 will be energized when the load on motor M6 increasesdue to passage of the forward end of the strip through stand S6. Ofcourse, when the trailing end of the strip passes through stands S1 and$6, the load relays lLR and 6LR, respectively, will become deenergizeddue to the decrease in the loads on motors M1 and M6.

' Load relay 1LR is provided with a pair of normally open contacts 44which, when closed, will energize relay lLRX having a pair of normallyopen contacts 46 and a pair of normally closed contacts 48. When loadrelay 6LR is energized, it will close its normally open contacts 54) toenergize the relay 6LRX having a pair of normally open contacts 52 and apair of normally closed contacts 54. When relays 6LR and 6LRX areenergized due to an increase in the load on motor M6 when the forwardend of the strip passes through stand S6, contacts 52 will close toenergize a time delay relay T after a predetermined amount of time haselapsed subsequent to the energization of relays 6LR and 6LRX. As willbe seen, the time delay of relay T is such that the forward end of thestrip will pass over run out table 36 'and become attached to coiler 40before the relay T becomes energized to close its normally open contacts58.

Connected across the output terminals of generator 66 is a magneticamplifier 60 which will produce an output signal to trip relay 62 whenthe voltage of generator G6 exceeds a predetermined level. age or speed)at which the relay 62 will be energized to close its normally opencontacts 66 and 67 is determined by a manually adjustable potentiometer64 coupled to the magnetic amplifier 60. Thus, the operator may manuallyadjust the point at which relay 62 will be energized to close contacts66.

Referring now to the pilot motor 34, it is provided with an externalfield winding 68, as well as a series winding 70, and is connected tothe output of an amplidyne regulator 72 having a winding 74 magneticallycoupled to an external control winding 76. Winding 76, in turn, isconnected. through resistor 78 to a manually adjustable potentiometer30, the arrangement being such that the' operator may manually adjustthe field produced by winding 76 and, hence, the output voltage ofamplidyne 72. It will be noted that when contacts 48 of relay lLRX areclosed, the potentiometer 80 is effectively shorted out The load (i.e.,voltand contacts 92 are open. When relay M-U is energized, contacts 92will close to complete a circuit betweenterm-inals 88 and 82 ofamplidyne 72 through contacts 92 of relay MU, motor 34 and contacts 84of relay M D. Un-

der these conditions, motor 34 will rotate the movable tap onpotentiometer 3th in a clockwise direction as shown in the drawings toaccelerate each of the motors M1, M6, etc., associated with the variousfinishing stands S1-S6. Similarly, when relay MD is energized, contacts90 will be closed to complete a circuit. from terminal 88 of amplidyne72, through motor 34 and contacts 86 of relay MU to terminal 82. Now,the movable tap on potentiometer 30 will be rotated in acounterclockwise direction as shown in the drawing to deceleratethemotors M1, M6, 7

etc. When the movable tap on potentiometer 30 rotates to its extremeclockwise position, it will open the normally closed contacts 93 of alimit switch 95. r

The system may be operated either automatically or semi-automatically.-Under automatic operation, the speeds of the stands Sl-S6 willLbeautomatically increased when the end of the strip becomes attached tocoiler 40. On the other hand, under semi-automatic operation, the pointat which the acceleration starts may be controlled manually by theoperator. If fully-automatic operation is desired, the switch 91 will beclosed and potentiometer 89. As was explained above, the positioning ofthe tap on potentiometer 80 thus determines the rate of acceleration ofthe various motors M1, M6, etc.

When the leading edge of the rolled strip enters the roll pass offinishing stand S6, the load on motor M6 will increase to energize loadrelay 6LR and close contacts 50. Closure of contacts 54) energizes relay6LRX to close its normally opencontacts 52 and open its normally closedcontacts 54. Since contacts 56 are now closed, a circuit is completed torelay T. This relay will be energized to close its contacts 58 after apredetermined amount of time has elapsed subsequent to the energizationof relay 6LRX. The time delay of relay T is'chosen'to coincide with theamount of time required for the leading edge of the strip to pass fromstand S6 to the coiler 40..

Thus, relay T will not pick up until the end of the strip is in thecoiler 40 and attache-d thereto.

When the end of the strip is attached to the coiler 40v and the contacts58 of relay "T close, acircuit is completed through switch 91, contacts58, contacts 106 of hold pushbutton switch H, contacts 46 of relay ILRX,which are now closed, and contacts 93 of limit switch 95 to the mill uprelay MU, as well as the mill down holding coil MDH. Thus, since relaysT and .ILRX are now both energized, relay MU will be energized to closecontacts 92 whereby the output of amplidyne 72 is applied to motor 34 torotate the movable contact on potentiometer 30 in a clockwise direction,the speed of rotation of this movable contact being determined by theposition of the contact on potentiometer 80 to control the rate ofacceleration of the mill. The mill will accelerate to full speed;whereupon the movable contact of potentiometer 30 reaches its extremeclockwise position to trip limit switch 95 and open contacts 93, therebydeenergizing the mill up relay MU and stopping the motor 34. When motor34 thus stops, the acceleration of motors M1, M6, etc., is also stoppedso that the mill is now operating at maximum speed, this speed beinggreater than the maximum permissible entry speed of the end of the stripinto the coiler 40. Since, however, the speed was not increased untilthe end of the strip was attached to the coiler, the problem of coilerentry at the high speed is eliminated.

During the main portion of the rolling procedure, the mill will continueto operate at high speed. When the trailing edge of the rolled strippasses through stand 81, the load on motor M1 will fall to deenergizerelays lLR and ILRX to open contacts 46 and close contacts 48. Withcontacts 48 closed, the maximum field will be produced in winding 76 onamplidyne 72 such that, when mill down relay MD is energized, the motor34 will rotate the movable contact on potentiometer 31 in acounterclockwise d-irection at maximum'speed to produce a maximum rateof deceleration in the motors M1, M6, etc. After the trailing edge ofthe strip passes through stand S6, the load on motor M6 will fall,thereby deenergizing relays 6LR and 6LRX to open contacts 52 whileclosing contacts 54. of course, deenergized.

When the motor M6 is at its maximum speed, the relay 62 will beenergized through magnetic amplifier 60 to close contacts 66 and 67.Relay 62 will remain energized until the output of generator G6 falls toa predetermined level, this level being determined by the position ofthe movable contact on manually adjustable potentiometer 64. Thus, if itis assumed that the trailing end of the strip has just passed throughstand 86, motor M6 will still be operating at a high speed so that relay62 will be energized to close contacts 66 and 67. Since switch 91 is nowclosed, a circuit will be completed through contacts 66, switch 91,contacts 54 of relay 6LRX, which is now deenergized, and contacts 104 ofpushbutton hold switch H to the mill down relay MD and holding coil MUH.Energization of mill down relay MD then closes contacts 90 while openingcontacts 84 to cause motor 34 to rotate the movable contact onpotentiometer 3%) in a counterclockwise direction from its extremeclockwise direction where it trips limit switch 95. The movable contacton potentiometer 30 will continue to rotate in a counterclockwisedirection until the speed of motors When contacts 52 open, the relay Tis, I

opened by the movable contact on potentiometer 30. In this manner, itwill be seen that by closing switch 94 the time at which the motors M1,M6, etc., begin accelerating may be delayed under the control of theoperator- That is, the motors 'wil not accelerate until the operator hasdepressed the pushbutton switch 100, notwithstanding the fact that aconsiderable amount of time may have elapsed since the entry of thestrip into the coiler 4%).

Similarly, the time at which deceleration of the motors M1, -M6, etc.,occurs, may be controlled by pushbutton switch @102 when thesemi-automatic switch 94 is closed. Thus, when switch .102 ismomentarily closed, a circuit will be completed through switch 94,contacts 54 of relay 6L-RX, which is now deenergized, and contacts 104of pushbutton switch H to the mill down relay MD which then closescontacts 90 to rotate motor 34 and the movable contact on potentiometerin a counterclockwise direction. In this latter case, the mill willcontinue to decelerate until contacts 67 are opened upon deenergizationof relay 62 at the speed determined by the position of the contact onpotentiometer 64.

The acceleration or deceleration of the mill may be stopped at any pointby depressing the hold pushbutton switch H. Thus, during acceleration ofthe mill, opening of contacts 106 will stop the acceleration processuntil these contacts again close. Similarly, the deceleration processmay be stopped for any period of time by depressing pushbutton switch Hto open contacts 104.

It can thus be seen that the present invention provides a method andapparatus for rolling hot strip wherein the speed of the mill isinitially maintained at a relatively low 3 value until the forward endof the strip is attached to a Nil-4M6 reaches a point where the relay 62is deener- For semi-automatic operation of the system, switch 94 a willbe closed while switch 91 remains open. Under these conditions, thepilot motor 34 will not he energized to rotate the movable tap onpotentiometer '39 in a clockwise direction until the pushbutton switch160 is closed. After the pushbutton switch 100'is closed and relay MU isenergized, the contacts 96 provide a holding circuit which will persistuntil contacts 93 of limit switch 95 are coiler, and thereafterincreased to a higher value to minimize the amount of time required forthe strip to pass through the mill.

Although the invention has been shown in connection with a certainspecific embodiment, it will be readily apparent to those skilled in theart that various changes in form and arrangement of parts may be made tosuit requirements without departing from the spirit and scope of theinvention.

We claim as our invention:

1. In a multi-stand tandem rolling mill of the type in which each standis provided with a separate electrical drive motor and a separategenerator for that motor together with a master pilot regulator foradjusting the output voltages of said generators and the speeds of saidmotors; the improvement which comprises first relay means actuable inresponse to an increase in the load on the drive motor for the firststand of the tandem rolling mill, second relay means actuable inresponseto an increase in the load on the drive motor for the last stand of thetandem rolling mill, third relay means operatively connected to saidsecond relay means and adapted to be actuated when a predeterminedamount of time has elapsed after actuation of the second relay means, adevice responsive to actuation of said first and third relay means forcausing said master pilot regulator to increase the output voltages ofsaid generators and thereby accelerate the respective motors on eachstand, fourth relay means actuable when the output voltage of thegenerator associated with the last tandem rolling mill stand increasesabove a predetermined level, and means actuable when second relay meansis deenergized and the fourth relay means is energized to cause saidmaster pilot regulator to decrease the output voltages of saidgenerators and thereby decelerate the motors on the respective stands ofthe rolling mill.

2. in a multi-stand tandem rolling mill of the type in which each standis provided with a separate electrical drive motor and a separategenerator for that motor; the improvement which comprises meansincluding an adjustable potentiometer for varying the output Voltages ofsaid generators and the speeds of said motors, a pilot motor for drivingsaid adjustable potentiometer, first relay means actuable in response toan increase in the load on the drive motor for the first stand of therolling mill, second relay means actuable in response to an increase inthe load on the drivemotor for the last stand of the rolling mill, thirdrelay means operatively connected to said relay means and adapted to beactuated when a predetermined period of time has elapsed after actuationof the second relay means, and fourth relay means responsive toactuation of the first and third relay means for causing said pilotmotor to adjust the potentiometer whereby the out,- put voltages of saidgenerators and the speeds of said motors are increased.

3. In apparatus for controlling a multi-stand tandem rolling mill of thetype in which each stand is provided with a separate electrical drivemotor and a separate generator for that motor; the improvement whichcomprises means including an adjustable potentiometer for regulating theoutput voltages of said generators and the speeds 'of said motors, apilot motor for driving said adjustable potentiometer, first relay meansactuable in response to an increase in the load on the drive motor forthe first stand of the rolling mill, second relay means actuable inresponse to an increase in the load on the drive motor for the laststand of the rolling mil], third relay means operatively connected tosaid second relay means and adapted to be actuated when a predeterminedamount of time has elapsed after actuation of the second relay means,fourth relay means actuable when the output voltage of the generatorassociated with the last stand in said tandem rolling mill exceeds apredetermined value, fifth tentiometer whereby the output voltages ofthe generators and the speeds of the motors are increased, and sixthrelay means actuable in response to deenergization of the second relaymeans and energization of the fourth relay means for causing said pilotmotor to drive the potentiometer whereby the output voltages of thegenerators and the speeds of the drive motors are decreased.

4. In a rolling mill comprising a plurality of stands in tandem, arun-out table at the discharge end ofthe mill and a coiler at thedischarge end of the run-out table, drive motors for the stands, and amaster pilot regulator for varying the speeds of, the drive motors; theimprovement comprising first means actuated when the work 4 enters thelast stand, second means actuated in response to actuation of the firstmeans and after the work enters the coiler, third means responsive toactuation of the second means adapted to cause the master pilotregulator to accelerate the drive motors, fourth means actuated when thetrailing end of the work leaves the last stand, and fifth meansresponsive to deactuation of the first means and actuation of the fourthmeans for causing the master pilot regulator to decelerate the drivemotors.

References Cited in the file of this patent UNITED STATES'PATENTS

1. IN A MULTI-STAND TANDEM ROLLING MILL OF THE TYPE IN WHICH EACH STANDIS PROVIDED WITH A SEPARATE ELECTRICAL DRIVE MOTOR AND A SEPARATEGENERATOR FOR THAT MOTOR TOGETHER WITH A MASTER PILOT REGULATOR FORADJUSTING THE OUTPUT VOLTAGES OF SAID GENERATORS AND THE SPEEDS OF SAIDMOTORS; THE IMPROVEMENT WHICH COMPRISES FIRST RELAY MEANS ACTUABLE INRESPONSE TO AN INCREASE IN THE LOAD ON THE DRIVE MOTOR FOR THE FIRSTSTAND OF THE TANDEM ROLLING MILL, SECOND RELAY MEANS ACTUABLE INRESPONSE TO AN INCREASE IN THE LOAD ON THE DRIVE MOTOR FOR THE LASTSTAND OF THE TANDEM ROLLING MILL, THIRD RELAY MEANS OPERATIVELYCONNECTED TO SAID SECOND RELAY MEANS AND ADAPTED TO BE ACTUATED WHEN APREDETERMINED AMOUNT OF TIME HAS ELAPSED AFTER ACTUATION OF THE SECONDRELAY MEANS, A DEVICE RESPONSIVE TO ACTUATION OF SAID FIRST AND THIRDRELAY MEANS FOR CAUSING SAID MASTER PILOT REGULATOR TO INCREASE THEOUTPUT VOLTAGES OF SAID GENERATORS AND THEREBY ACCELERATE THE RESPECTIVEMOTORS ON EACH STAND, FOURTH RELAY MEANS ACTUABLE WHEN THE OUTPUTVOLTAGE OF THE GENERATOR ASSOCIATED WITH THE LAST TANDEM ROLLING MILLSTAND INCREASES ABOVE A PREDETERMINED LEVEL, AND MEANS ACTUABLE WHENSECOND RELAY MEANS IS DEENERGIZED AND THE FOURTH RELAY MEANS ISENERGIZED TO CAUSE SAID MASTER PILOT REGULATOR TO DECREASE THE OUTPUTVOLTAGES OF SAID GENERATORS AND THEREBY DECELERATE THE MOTORS ON THERESPECTIVE STANDS OF THE ROLLING MILL.